Lecture notes for BS1050 An introduction to genetics (BS1050)
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Course
BS1050 An introduction to genetics (BS1050)
Institution
University Of Leicester (LE)
These are compiled notes from the genetics module you'll do in your first year. These are general notes that cover the whole subject to help fill in the gaps in learning.
BS1050 Notes
Hardy-Weinburg equalibrium
Allele frequencies measure how much of the population have a certain trait.
A human Phenotype can be shifted by the change of one sequence on the genome
Mendels ratio of phenotypes of progeny of heterozygotes is 3:1 meaning there will be 1 of
the first phenotype, 2 for the second and 1 for the third.
This only affects plants however
Instead humans were in the hardy-weinburg equalibrium
This is a state in which the genotype will remain the same from generation to generation
It however assumes
1. The mating is random according to genotype
2. The population size is infinite (or at least very large)
3. No mutation
4. No natural selection
5. No migration
This means that genotypes can be calculated from this. This means that the number of
carriers of a genetic disease can be calculated.
This means a small number of observed carriers can be extrapolated to a larger population
A chi-square test is used to calculate the accuracy of this though. There are many
populations that aren’t in this equalibrium.
If the X2 number is higher then the critical value from the calculator then HWE is not true.
Vice versa is true as well
Migration
Migration brings new alleles into a population from the outside
This is called gene flow.
Migration helps keep populations affloat and working. It prevents inbreeding and promotes
growth.
Modelling migration is difficult but it can be done.
One model is a mainland to island model. There are others too though.
, The main concequence of this though is the admixture of populations. This can be seen in
the atlantic slave trade and how it caused the genetic make up of the Americas to be much
more diverse.
The admixture within the population will be diluted over time but it still will be affected in
some way.
Terms in Genetics
Eukaryotes: multicelled organisms
Diploid: Have two copies of a gene
Haploid: Have one copy
Gene: Fragment of DNA that encodes for RNA
Allele: An alternate form of the same gene
Homologues: Genes related by decent
Genotype: Genetic composition of a creature
Phenotype: Traits that are shown
Haplotype DNA variations (Polymorphisms): These are traits that tend to be inherited
together
Heterozygote: has differing alleles
Homozygote: Has same alleles
Incomplete dominance is when the heterozygous has a phenotype that is in between the
phenotypes of the two homozygous.
This must not be confused with codominance which, is when both alleles of the
heterozygous contribute equally to the phenotype.
A major example of this is the ABO blood system 4 phenotypes: A, B, AB, O 2 antigens A and
B One gene: I. Three alleles: IA, IB and iO (recessive)
Dominant mutations: dwarfism is an example of this. If a parent is a carrier then the child
has a 50% chance of inheriting the condition.
If they have the condition, or have both of the dwarfism alleles then they have a 75%
chance of inheriting the condition.
Penetrance and expressivity
Identical genes produce different expression patterns
This can be explained by the fact that the expression of individual genes is influenced by
other genes in the genome of that particular individual, i.e., the genetic background, and by
its interactions with the environment.
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